Uninstall anti-virus software from the virtual machine. Or you can add “coherence.exe” and “prl_hook.dll” in antivirus exclusions.
Do not forget to install the anti-virus software back, once the problem is resolved.

Step 4 - Reinstall Parallels Tools

As already mentioned above, the issue may be caused by corrupted video drivers inside the virtual machine. Drivers for virtual devices are supplied by Parallels Tools package. Please (re)install Parallels Tools in your virtual machine using these instructions: